Myth might be a strong term, since I haven't done any of the requisite research to really support my position, but it makes for a good title, and I'm just going to be bold and go out on a hunch.
It seems fairly well agreed upon by many in the industry/field of study that there is a critical period for learning language and that when a child matures beyond a certain age, their propensity for learning a language begins to drop drastically.
I'm not here to argue with the fairly obvious outcomes: yes, we often see young learners making progress more rapidly than we do post adolescent learners. I am however going to put forward some suggestions or possibilities to consider rather than the notion that this is a biological issue and that the brain simply becomes less effective at language learning as we age.
One of the reasons I refuted this notion to begin with was simply because it is so uncharacteristic, so counter-intuitive; generally, we see our brain develop in the early years to become more powerful, more efficient, more effective at learning and doing various things. Why would the opposite be true? We see babies develop faculties for recognising people, for being self aware, would it really follow that meanwhile, they would be losing the ability to learn language?
But again, it's difficult to argue with the outcomes, and like so many of these things that we cannot explain, we can only take our assessments from observable outcomes, as we don't yet understand everything (if anything) that is going on in the brain—which, consequently, we then often guess at. So I have tried to think what else might explain these clear patterns of reduced efficiency in language learning over time, if not deteriorating brainpower.
In fact, after thinking about it in these terms, it doesn't actually seem so outrageous or baffling. I can think of a number of practical, real world factors that might lead to such results, and I shall briefly explore some of them here.
This is something I talk about in a lot of my teacher training as a factor that is so often underestimated when trying to identify obstacles to learning. I always try to emphatically point out and reiterate the likelihood that the students in the classroom are not actually giving one hundred percent of their attention to the teacher and the lesson. There could be a thousand and one other things on the students' minds, all vying for attention and providing distractions.
Typically, what I feel the need to remind teachers of is the fact that younger students, adolescents for example, have just as much distraction to deal with as you as an adult do. Do not forget what it was like to be a student, and do not forget just how important to you were the things that you now wish your teenage students would just get over! However, that being said, it is probably fair to say that with age, responsibility increases, and with it so does preoccupation.
While even a young learner has a lot to deal with as he learns how to navigate the world, he does not have to consider a great many preoccupations or unfinished businesses and can be fully focused on the task at hand. In fact, one of the faculties that the brain is yet to develop in the early years is the sense of cause and effect or consequence, so it is much easier for a language-acquiring infant to "be in the moment", dealing with the present problem.
Teens, as said earlier, have all those adolescent problems clouding their mind so that while they should be focused on their lessons, they are in fact preoccupied by things like their popularity, that guy or girl they like, the fact that they have just had a fight with their best friend, and also the anxiety that grows around exams and class reports. Add a decade, and you can also add things like taxes, supporting a family, raising children of your own, getting that promotion at work and so much more.
Is it any wonder then that more mature students demonstrate slower learning?
When we look at early learners and their language learning progress, we are for the most part looking at people learning their first language, though a decent number of studies and research have also been done into bilingual children as well. Of course, when we look at mature students, we are almost invariably looking at fluent first-language (L1) speakers trying to learn a second language (L2).
What this means for starters is that we are not really assessing the same thing when we look at progress in most young learners and progress in most adult learners. Learning your first language almost always means the same thing as learning your home or primary language. Learning any additional language, for the majority of cases, means learning a secondary or even foreign language.
That much might seem obvious, but that doesn't mean it doesn't need thinking about. Learning your home language means that everybody around you is using it, all the the time in fact. Not only that, but they are using it directly at you, and almost everybody is very consciously and very overtly taking on the roll of facilitator, trying very hard to make the language as accessible to you as possible (demonstrated beautifully in research conducted by Deb Roy).
Meanwhile, learning a second language as an adult learner is often not the same. First of all, it is not likely that you will be so fully immersed in the language, as it is usually not the local language, unless you move to a new place geographically or live in a heavily multicultural place to begin with. However, interestingly this is my own experience, and I found that I have been quite capable of learning the language to a practical level of fluency (perhaps B2) in those circumstances, which far more closely represent the circumstances of young learners learning first languages.
Furthermore, even if the exposure is higher than normal, most adults do not receive the same level of tutoring from those around them as a young learner does. Adults are not likely to find themselves given so much guidance or concession during their learning. They will not meet as much patience or persistence with their interlocutors. So the language environment itself, even with high exposure, will be much more resistant/hostile to the adult learner than to the young learner.
Another factor that needs to be carefully considered when comparing first language learning with second language learning is L1 Interference. This is the notion that when learning a second language, we are stunted by the existing knowledge of our first language, in particular in two areas: where the grammatical logic of the latter appears to clash with the former and where pronunciation requires different physical sound production and patterns.
For example, any two languages with different syntactic norms will seem to contradict one another, which can make learning the newer, second language more difficult after spending the rest of your life up to that point learning how language works only to find that it works differently in other parts of the world.
A young learner learning the first language does not have the burden of a pre-existing linguistic structure, and even a bilingual young learner learning two languages does not have an established understanding of language getting in the way of his or her learning. So once again, our expectations of mature second language learners should be readdressed if we want the comparison to be a fair one.
The final problem I want to explore is that of motivation. The motivations for learners of different ages are of course extremely different.
Young learners are motivated primarily by an almost do-or-die scenario, wherein they absolutely need to develop language in order to communicate with the people around them. If they do not learn any language at all, they will find it very difficult to negotiate even the simplest of things, such as acquiring the basic needs for survival.
Young learners realise as they begin to develop language skills just how much more efficient their communication becomes, and thus they work to learn more. A combination of all of the factors discussed above and this kind of motivation makes for a very effective learner. The do-or-die scenario can exist for adolescent and mature learners in specific cases, but generally people's primary language environment remains L1, and thus their survival relies largely on L1.
This is a fairly extrinsic motivation, but it also coupled with a high sense of achievement for most young learners, especially when that is so often expounded by intense positive feedback from caregivers. This can generate feelings of joy linked directly to progress in learning language, which is then fairly self-perpetuating.
Motivation for adolescent learners to learn a second language are often either social or academic. Children and teenagers moving into a new language environment are rarely isolated from their L1 entirely, but often find it favourable to learn the L2 for the sake of making friends and just generally 'fitting in'. The level of social anxiety that a particular individual experiences will affect just how powerfully motivating this is. For some, this can feel relatively close to do-or-die.
Students choosing to study overseas are another group of adolescents who might choose to learn a second language. Here the motivation is quite different and somewhat more extrinsic, which usually means less effective. Typically, this type of motivation is based on the negative outcomes of failure rather than the positive outcomes of success, and such motivation often starts out quite powerful but the fear of bad grades and the novelty of good grades usually fades over time.
For mature learners, the reasons for learning are generally either professional, social or purely for leisure. Learning a second language in order to either get a promotion or work overseas are common motivations for adult learners and are modelled on the same mechanics as the academic motivation outlined above.
Socially, most mature learners will already have a fairly well-developed network of fellow L1-speakers, so learning a second language in order to expand this network is in the majority of cases far from essential, and will require a high level of intrinsic motivation to really show progress.
In fact, intrinsic motivation is far more necessary for mature learners than it is for younger learners and certainly for learners in what is currently considered the critical period. Young learners and adolescents obviously benefit from intrinsic motivation, and it it the presence or absence of this that generally explains the difference in progress between two young learners or two adolescent learners. However, for these groups, if intrinsic motivation is not present from the start, other motivations can often be enough to get the ball rolling, and then sense of achievement, positive feedback or just general enjoyment can generate intrinsic motivation as an emergent property.
However, in most cases, the extrinsic motivations present in a mature learners life are fewer and far less motivating. Often, if some form of intrinsic motivation is not present to begin with, the mature learner will either give up early on or not even start in the first place. This is not then a matter of biology but rather, once again, one of environment.
So it seems to me quite obvious that to expect an adult learner to show the same progress as a young learner is somewhat unreasonable, based on the various differences in the language environment and the patterns of learning behaviour. To look at this and postulate a natural, universal depreciation in brain specialisation seems to me to be quite a leap, especially when our general understanding of early brain development so far suggests the exact opposite, i.e. increased functionality and specialisation over time.
And when there is no biological evidence apparent to support the idea that we lose this functionality and specialisation, why are we so willing to accept the hypothesis? Why, when the reasons suggested in this article are on the other hand so readily observable?
If a patient with a broken leg came into a doctor's clinic, and the doctor knew that the patient had just had an accident while playing football, it would seem preposterous for the doctor to hypothesise a pre-existing biological defect as the probable cause of the injury; yet, this is essentially analogous to the theory of the critical period.